70 



J. W. COLEMAN, A. S. HOLT, E. I. RAHINOWITCH 



back were necessitated by difficulty of discriminating between fluc- 

 tuations in the fluorescence excited by the (very intense) actinic light 

 and changes in the (much weaker) measuring light. After the ninth 

 stage of amplification, the signal was rectified, compared, and, 

 by means of a balanced-plate cathode-follower, fed into a Brown 

 recorder (as in Duysens' instrument) . 



^f measured =/"(a) 



Aex=/'(M 



650 



700 



A in rriM 



750 



Fig. 1. Reversible changes in Chlorella spectrum during illumination. Dashed line: 

 estimated correction for fluorescence. 



Chlorella cells, grown in our laboratory, were washed, suspended 

 in carbonate, and refrigerated until needed. The cells were used as taken 

 from the refrigerator (optical density of suspensions, 0.45, at 680 

 mju, corrected for scattering). The actinic light was furnished by a 

 tungsten lamp (1000 watt, GE 1000T20, 120 volts); the entire side of 

 the cuvette was uniformly illuminated. Before using a sample for 

 systematic measurement, a check was made at several selected wave- 



